In the design of lighting systems of the type used for illuminating roadways, parking lots, warehouses and the like, a primary goal is to obtain uniform illumination of the area covered by each individual light fixture or luminaire in the system to avoid bright spots and dark spots on the surface being illuminated. It is especially desirable to provide a fixture capable of producing a relatively uniform light intensity over rectangular or square areas, such that the corners of the square receive substantially the same amount of illumination as the sides of the square.
It also is desirable to minimize, as much as possible, the total amount of energy which is consumed by any lighting system, since energy costs in recent years have increased substantially. Because of the low energy consumption which they require, high intensity discharge (HID) lamps have found widespread acceptance in commercial applications. HID lamps produce strong light patterns in planes perpendicular to the lamp axis so that, typically, such lamps are mounted in planes perpendicular to the plane of the surface to be illuminated. As a result, the reflector segments of the luminaire are uniformly spaced around the lamp axis.
When a pattern of luminaires is designed to illuminate a given area, such as a parking lot, the lighting engineer has a limited number of choices of light distributions which are effected by employing pole layouts in various patterns. For example, if the pole layout is in the form of squares, it is desirable to employ luminaires, each one of which produces a square pattern of light. Consequently, the square patterns of light then may be nested against each other to provide complete coverage of the area to be lighted In other situations, where the layout of the light poles may be on a rectangular pattern, a rectangular pattern of light from the individual luminaires is beneficial. Whenever a luminaire produces a pattern of light which does not fit the exact area to be lighted, a problem is created with spilled light, lighting unwanted areas with consequent power wastage, or portions of the area to be lighted may have inadequate illumination.
In the past, attempts have been made to adjust the patterns of light emanating from a luminaire by the provision of segmented adjustable reflector sections in the luminaire. A typical luminaire of this type, used with an incandescent lamp, is disclosed in the patent to Tolbert, U.S. Pat. No. 3,213,271. This patent is directed to a luminaire used for lighting residential streets and includes a pair of compound curved reflector segments, mounted on opposite sides of the bulb. These reflector segments each are individually adjustable by sliding them in grooves to effect both vertical orientation or tilting, and horizontal positioning about the bulb. As a result, reflected light is shifted within a limited range upwardly or downwardly, to direct the beam of light in the appropriate directions on a hilly road, and also to adjust the beam laterally to maximize the direction of the beam on a curve in the road, when the light fixture is located at such a curve. This fixture is not intended for providing uniform illumination of a square or rectangular area, however.
Another luminaire, with adjustable reflectors in it for the purpose of providing an assymetrical illumination of the region beneath the fixture is disclosed in the patent to Mousset, U.S. Pat. No. 4,261,029. The fixture of the Mousset patent mounts a lamp in an eccentric position within the fixture and locates adjustable reflector elements on opposite sides of the light-producing planes of the lamp to direct the light from the fixture off to one side of the region located beneath the fixture. There is no attempt, in the device disclosed in this patent, to compensate for reduced illumination in the corners of square or rectangular areas to be illuminated.
A luminaire utilizing an HID bulb mounted in a plane with its axis parallel to the plane of the open side of the luminaire housing is disclosed in the patent to Lewin, U.S. Pat. No. 4,575 788. The luminaire of the Lewin patent includes a housing which has four identical primary compound-curved reflector sections oriented with two sections on each side of the lamp, to produce major projections of the light emanating from the luminaire diagonally of the longitudinal axis of the lamp in a horizontal plane. This creates a generally square or rectangular distribution of light on the surface to be illuminated. Since HID lamps inherently have reduced lamp intensity along the direction of the axis of the lamp, auxiliary reflector sections are placed at the ends of the bulb and interconnect the four main reflector sections, to create an increase in the light projected along the lamp axis. This increase compensates for the reduction in inherent lamp intensity along its axis. The specific arrangement of reflector sections disclosed in the Lewin patent, however, is unique to the somewhat non-standard "horizontal" mounting of the lamp in the fixture. The Lewin luminaire does not have application to an HID lamp which is mounted with its axis perpendicular to the open side of the luminaire housing.
It is desirable to provide a luminaire utilizing either an HID light source or an incandescent light source, which is capable of producing relatively uniform illumination of a square or rectangular area, which utilizes a relatively small number of parts, and which is simple to construct.